G-9 GLOSSARY Elastomer(Section 10. 11): A synthetic polymer that possesses aryne intermediate In the second stage, nucleophilic addi- tion to the aryne yields the product of the reaction. Electromagnetic radiation(Section 13. 1): Various forms of ra- Elimination bimolecular (E2)mechanism (Section 5.15): diation propagated at the speed of light. Electromagnetic Mechanism for elimination of alkyl halides characterized radiation includes (among others) visible light; infrared, ul- by a transition state in which the attacking base rer traviolet and microwave radiation: and radio waves. cos- proton at the same time that the bond to the halide leaving group is broken. Electron affinity(Section 1. 2): Energy change associated with Elimination unimolecular (E1)mechanism(Section 5.17 the capture of an electron by an atom Mechanism for elimination characterized by the slow for Electronegativity (Section 1.5): A measure of the ability of an mation of a carbocation intermediate followed by rapid loss atom to attract the electrons in a covalent bond toward it- of a proton from the carbocation to form the alkene. self. Fluorine is the most electronegative element. Enamine (Section 17. 11): Product of the reaction of a sec- Electronic effect (Section 5.6): An effect on structure or reac- ondary amine and an aldehyde or a ketone. Enamines ar tivity that is attributed to the change in electron distribution characterized by the general structure that a substituent causes in a molecule Electron impact (Section 13. 21): Method for producing posi- C=CR tive ions in mass spectrometry whereby a molecule is bom- 18-Electron rule(Section 14. 14): The number of ligands that Enantiomeric excess(Section 7.4): Difference between the can be attached to a transition metal are such that the sum of percentage of the major enantiomer present in a mixtur and the percentage of its mirror image. An optically pure trons of the metal equals 18 material has an enantiomeric excess of 100%o. A racemi Electrophile (Section 4.10): A species(ion or compound) that mixture has an enantiomeric excess of zero an act as a Lewis acid, or electron pair acceptor; an"elec- Enantiomers(Section 7. 1): Stereoisomers that are related as an tron seeker " Carbocations are one type of electrophile bject and its nonsuperimposable mirror image Electrophilic addition(Section 6. 4): Mechanism of addition in Enantioselective synthesis(Section 27. 4): Reaction that con- which the species that first attacks the multiple bond is an verts an achiral or racemic starting material to a chiral prod electrophile("electron seeker") uct in which one enantiomer is present in excess of the Electrophilic aromatic substitution (Section 12.1): Fundamen- tal reaction type exhibited by aromatic compounds. An Enantiotopic(Section 13.6): Describing two atoms or groups electrophilic species(Et)attacks an aromatic ring and re- in a molecule whose environments are nonsuperposable places one of the hydrogens mirror images of each other. The two protons shown in bold Ar-H+E—Y—)Ar-E+H-Y in CHa CH,Cl, for example, are enantiotopic. Replacement of first one, then the other, by some arbitrary test group Electrophoresis(Section 27.3): Method for separating sub- yields compounds that are enantiomers of each other. stances on the basis of their tendency to migrate to a posi Endothermic(Section 1. 2): Term describing a process or reac- tively or negatively charged electrode at a particular pH Electrostatic attraction ( Section 1.2): Force of attraction be Enediyne antibiotics(Section 9.4): A family of tumor-inhibit tween oppositely charged part ing substances that is characterized by the presence of a Electrostatic potential (Section 1.10): The energy of interac C≡C-C=C-C≡ C unit as part of a nine- or ten tion between a point positive charge and the charge field of membered ring. a molecule. The electrostatic potential is positive for the in- Energy of activation(Section 3. 2): Minimum energy that a re teraction between the point positive charge and the mole acting system must possess above its most stable state in or cules electrons and negative for the interaction er to undergo a chemical or structural change nuclei Enol (Section 9.12): Compound of the type Elementary step(Section 4.7): A step in a reaction in which each species shown in the equation fo participates in the same transition state. An eleme is characterized by a single transition state. Elements of unsaturation: See index of hydrogen deficiency. Enols are in equilibrium with an isomeric aldehyde or ke B-Elimination (Section 5.8): Reaction in which a double of tone, but are normally much less stable than aldehydes and ent atoms(See dehydration, dehydrogenation, dehydro. Enolate ion( Section 18.6): The conjugate base of an enol halogenation, and double dehydrohalogenation.) Enolate ions are stabilized by electron delocalization Elimination-addition mechanism(Section 23.8): Two-stage first stage, an aryl halide undergoes elimination to form the mechanism for nucleophilic aromatic substitution. In RC=CR2<>RC-CR? Forward Main Menu TOC Study Guide Toc Student OLCMHHE WebsiteG-9 GLOSSARY Elastomer (Section 10.11): A synthetic polymer that possesses elasticity. Electromagnetic radiation (Section 13.1): Various forms of ra￾diation propagated at the speed of light. Electromagnetic radiation includes (among others) visible light; infrared, ul￾traviolet, and microwave radiation; and radio waves, cos￾mic rays, and X-rays. Electron affinity (Section 1.2): Energy change associated with the capture of an electron by an atom. Electronegativity (Section 1.5): A measure of the ability of an atom to attract the electrons in a covalent bond toward it￾self. Fluorine is the most electronegative element. Electronic effect (Section 5.6): An effect on structure or reac￾tivity that is attributed to the change in electron distribution that a substituent causes in a molecule. Electron impact (Section 13.21): Method for producing posi￾tive ions in mass spectrometry whereby a molecule is bom￾barded by high-energy electrons. 18-Electron rule (Section 14.14): The number of ligands that can be attached to a transition metal are such that the sum of the electrons brought by the ligands plus the valence elec￾trons of the metal equals 18. Electrophile (Section 4.10): A species (ion or compound) that can act as a Lewis acid, or electron pair acceptor; an “elec￾tron seeker.” Carbocations are one type of electrophile. Electrophilic addition (Section 6.4): Mechanism of addition in which the species that first attacks the multiple bond is an electrophile (“electron seeker”). Electrophilic aromatic substitution (Section 12.1): Fundamen￾tal reaction type exhibited by aromatic compounds. An electrophilic species (E) attacks an aromatic ring and re￾places one of the hydrogens. Electrophoresis (Section 27.3): Method for separating sub￾stances on the basis of their tendency to migrate to a posi￾tively or negatively charged electrode at a particular pH. Electrostatic attraction (Section 1.2): Force of attraction be￾tween oppositely charged particles. Electrostatic potential (Section 1.10): The energy of interac￾tion between a point positive charge and the charge field of a molecule. The electrostatic potential is positive for the in￾teraction between the point positive charge and the mole￾cule’s electrons and negative for the interaction with the nuclei. Elementary step (Section 4.7): A step in a reaction mechanism in which each species shown in the equation for this step participates in the same transition state. An elementary step is characterized by a single transition state. Elements of unsaturation: See index of hydrogen deficiency. -Elimination (Section 5.8): Reaction in which a double or triple bond is formed by loss of atoms or groups from adja￾cent atoms. (See dehydration, dehydrogenation, dehydro￾halogenation, and double dehydrohalogenation.) Elimination—addition mechanism (Section 23.8): Two-stage mechanism for nucleophilic aromatic substitution. In the first stage, an aryl halide undergoes elimination to form an Ar±H E ±Y Ar±E H ±Y aryne intermediate. In the second stage, nucleophilic addi￾tion to the aryne yields the product of the reaction. Elimination bimolecular (E2) mechanism (Section 5.15): Mechanism for elimination of alkyl halides characterized by a transition state in which the attacking base removes a proton at the same time that the bond to the halide leaving group is broken. Elimination unimolecular (E1) mechanism (Section 5.17): Mechanism for elimination characterized by the slow for￾mation of a carbocation intermediate followed by rapid loss of a proton from the carbocation to form the alkene. Enamine (Section 17.11): Product of the reaction of a sec￾ondary amine and an aldehyde or a ketone. Enamines are characterized by the general structure Enantiomeric excess (Section 7.4): Difference between the percentage of the major enantiomer present in a mixture and the percentage of its mirror image. An optically pure material has an enantiomeric excess of 100%. A racemic mixture has an enantiomeric excess of zero. Enantiomers (Section 7.1): Stereoisomers that are related as an object and its nonsuperimposable mirror image. Enantioselective synthesis (Section 27.4): Reaction that con￾verts an achiral or racemic starting material to a chiral prod￾uct in which one enantiomer is present in excess of the other. Enantiotopic (Section 13.6): Describing two atoms or groups in a molecule whose environments are nonsuperposable mirror images of each other. The two protons shown in bold in CH3CH2Cl, for example, are enantiotopic. Replacement of first one, then the other, by some arbitrary test group yields compounds that are enantiomers of each other. Endothermic (Section 1.2): Term describing a process or reac￾tion that absorbs heat. Enediyne antibiotics (Section 9.4): A family of tumor-inhibit￾ing substances that is characterized by the presence of a CPC±CœC±CPC unit as part of a nine- or ten￾membered ring. Energy of activation (Section 3.2): Minimum energy that a re￾acting system must possess above its most stable state in or￾der to undergo a chemical or structural change. Enol (Section 9.12): Compound of the type Enols are in equilibrium with an isomeric aldehyde or ke￾tone, but are normally much less stable than aldehydes and ketones. Enolate ion (Section 18.6): The conjugate base of an enol. Enolate ions are stabilized by electron delocalization. RCœCR2 W O RC±CR2  O O RCœCR2 W OH R2CœCR W NR 2